Semiconductor image sensors are used to sense radiation such as light. Complementary metal-oxide-semiconductor (CMOS) image sensors (CIS) and charge-coupled device (CCD) sensors are widely used in various applications such as digital still camera or mobile phone camera applications. These devices utilize an array of pixels in a substrate, including photodiodes and transistors, that can absorb radiation projected toward the substrate and convert the sensed radiation into electrical signals.
A back side illuminated (BSI) image sensor device is one type of image sensor device. These BSI image sensor devices are operable to detect light projected from the backside. The BSI image sensors may have metal shields formed over reference pixels on the back side, so as to prevent light from reaching the reference pixels. Traditional semiconductor image sensor devices may experience large amounts of stress fluctuations caused at least in part by the existence of these metal shields. The stress within the image sensor devices can result in poor dark current performance of the image sensor.
Therefore, while existing semiconductor image sensors have been generally adequate for their intended purposes, they are not entirely satisfactory in every aspect.